Electronic endoscope systems are widely used in medical diagnoses. An electronic endoscope system is composed of an electronic endoscope having an insert section to be inserted in a body cavity of a patient and a processing device connected to this electronic endoscope. The processing device generates an endoscope image based on image signals received from an image sensor mounted to a distal portion of the insert section of the electronic endoscope. The processing device performs image processing to the endoscope image, and then outputs the endoscope image to a monitor. A doctor observes the body cavity and makes diagnosis, or treats the patient using a medical instrument projected from a medical instrument outlet of the distal portion of the insert section while viewing the endoscope image displayed on the monitor.
When the image sensor mounted to the distal portion of the insert section is positionally displaced from its correct mounting location, and/or rotationally displaced from its correct mounting orientation, the endoscope image displayed on the monitor is also positionally and/or rotationally displaced. As a result, the medical instrument projected from the medical instrument outlet is not displayed in a normal position on the monitor, making the endoscope awkward to use. Moreover, endoscopes, regardless of optical or digital type, have achieved high zoom magnification due to increase in the number of pixels in the image sensor. When the endoscope zooms in with its image sensor displaced from the center, the displacement amount of the image from the center also increases. As a result, the zoomed area is displaced from the intended area, which also makes the endoscope awkward to use. Thus, improvement on mounting location accuracy of the image sensor is required so as to reduce the displacement amount under higher magnification. In addition, a diameter of the endoscope is becoming smaller and smaller to reduce physical burden on a patient. Accordingly, the size of the image sensor is reduced and pixels are arranged at high densities with narrower spacing, increasing the displacement amount on the light receiving surface of the image sensor even though the mechanical displacement amount is unchanged. Thus, it is required to align the image sensor with the correct mounting location with a high degree of accuracy.
To solve the above-described problems, an imaging device for an endoscope according to Japanese Patent Laid-Open Publication No. 10-028233 has a position adjustment mechanism for adjusting a position of an image sensor mounted to a distal portion of an insert section in horizontal, vertical, and rotational directions. With the use of this position adjustment mechanism, the image sensor is aligned with a correct mounting location and orientation.
Japanese Patent Laid-Open Publication No. 11-290269 discloses a solid state imaging device for positioning and fixing an objective lens group forward of an image sensor. By utilizing this art for positioning and fixing the image sensor, the image sensor is aligned with a correct mounting location and orientation. An electronic endoscope disclosed in Japanese Patent Laid-Open Publication No. 2001-086378 has a fixing frame (see the fourth example) for positioning the image sensor. With the use of the fixing frame, the image sensor is aligned with a correct mounting location and orientation.
In the above publications No. 10-028233, 11-290269, and 2001-086378, the image sensor is aligned using the mechanical structures. Therefore, the mounting location accuracy of the image sensor is easily improved, although it has limitations. When the number of pixels in the image sensor further increases, the mechanical structures disclosed in the above publications may not be able to cope with the improvement on zooming alignment required due to the higher magnification of the electronic zoom, and improvement on the mounting location accuracy required due to downsizing of the image sensor in an electronic endoscope with a smaller diameter. In particular, in Japanese Patent Laid-Open Publication No. 10-028233, an inspector manually carries out the alignment using the position adjustment mechanism. Therefore, the mounting location accuracy of the image sensor depends on the skill of the inspector. In addition, in the above publications No. 10-028233, 11-290269, and 2001-086378, the mechanical structures increase production costs.